3 replies to this topic

[colt16]

Dear all, 

 

How complicated is it to convert a non-VFD motor to a VFD? Or alternatively reduce the speed of a motor?Can it be done with minimal investment? e.g. just a simple power reducer to the motor for the second case.

 

I think one of my plant's air blower is over-sized and therefore providing too much air to a thermal oxidizer. Hence the thermal oxidizer is unable to reach its operating temperature.

 

A suction damper could also work but there is not a lot of space.

[pavanayi]

If I recall correctly, such a modification is easy as the changes are done in the substation and not in the field. A quick call to the likes of ABB might provide you with some reliable information.

Maybe another member has first hand experience.

[Saml]

As a chemical engineer my knowledge comes from interacting with people in the electricity departments.

 

The main think they've told me everytime we talked about VFDs is that overheating of the motor is one of the problem. You have lower cooling because fan spins at lower speed. And you have more heat disipation because the VFD is not a "pure sine" signal but a series of pulses, so you have high frequency harmonics that dissipate energy inside the motor. For this service they recommended to specify an "inverter duty" motor.

 

Then you have all the questions of the electrical noise in the existing motor control center and the effect on protections.

 

And finally, VFD are more vulnerable to electrical system noise (like the activation of an autorecloser) and shuts down when a classic contactor with 0.5 seconds delay can keep the unit running.

[colt16]

Okay thanks for all the responses.